Fluid-pressure-operated tool



; Aug. 16, 1927.

v 2 Shays- Sheet 1 1J77072702Z I E. H. SHAFF FLUID PRESSURE OPERA TEDTOOL Filed Avril 5 1920 Aug. 16, 1927; 1,639,313

E. H. SHAFF I FLUID PRESSURE DPERATED TOOL Filed April 5 1920 2Sheets-Sheet 2 Patented Aug. 1e, 1927.

ERNEST H. snare, or GRAND Haven, MICHIGAN, ASSIGNOR r WILiiIAM H.KELLER,

PATENT OFFICE.

INCL, OF GRAND HAVEN, MICHIGAN, A CORPORATION OF MICHIGAN.

FLUID-PRESSURE-OPERATED TOOL.

' Application filed April 5 this type as heretofore manufactured, the.

return stroke or up stroke of the piston has been cushioned by a body ofdead air which is trapped in the rear or upper end of the piston chamberbehind or above me live air inlet through which air is introduced intothe piston chamber to drive the piston on its working stroke. The air inthis cushion chamber performs no function except to cushion the pistonand start it back on its forward or working stroke and inasmuch as newlive air must be supplied to fill this chamber at each stroke, there maybe said to be a certain amount of air wasted for cushioning purposesonly. Furthermore, the cushion chamber adds to the length of the hammerfor a given length of piston stroke.

It is one of the objects of my invention to eliminate such a. specialcushioning chamher and to provide a construction whereby the piston willbe cushioned upon live air admitted at the extreme rear or upper end ofthe piston chamber. To this end I aim to provide a structure in whichthe main valve will be moved forwardly-in a prompt and positive mannerduring the retur stroke of the piston so as to insure the open ing ofthelive air inlet at the rear end of the piston chamber at the proper timeto provide a body of live air against which the piston strikes attherear end of its stroke.-

Tn addition to eliminating the special space of the prior tools forcushioningpurposes my construction has the important advantage that thebody of air which cushions the piston is immediately active to start thepiston on its working stroke, being supple.- mented as the piston mevesforwardly by an increasing amount of live air through the inlet so thatthe impetus on the piston tending to move it on its working stroke isimmediate and continuous. This differs from prior tools infthatin thelatter the first impetus to the piston on its working stroke is thatgiven by the elasticity of the trapped air in the special cushioningchamber, while the real force or power for riving the piston isnotexerted thereon until 1920.: Serial No. 371,445.

the, piston has moved forwardly a sufficient distance to uncover theliveair inlet.

Another object of the invention is to provide an improved constructionwhich will insure a more prompt, rapid and positive shifting of thevalvemember than has been possible with tools heretofore known, and in whichthis desired action of the valve will be independent of whether thevalve member fits quite tightly or rather loosely in its casing. Thisobject is accomplished by so constructing the valve mechanism and theports and passages in connection therewith that the effective workingpressurevtending to move the valve toward the desired position and holdit there will be quite high. By effective working pressure ismeant thedifference between'the opposing pressures on the valve member actingupon the respective areas of the working faces of said member. The lowerthe opposing force. the greater is the corresponding effect of themoving and holding force. It is one of the ims of my invention tominimize the force opposing the movement ,of the valve. in

either direction. and the maintenance of the Another general obie'ct ofthe invention is to produce'a tool which is simpler in con struction,moreetlicient in operation and more durable than tools of this characternow known.

A further object is to produce an improved tool which will deliverheavier faster blows than tools now known. This object is accomplishedby so constructing the tool that the force of the live motive fluid uponthe piston in the forward movement thereof will follow the pistonthrough a greater portionof its stroke than in prior tools, and so thatthe control valve will be shifted more promptly even with the increasedtime of maintenance of full working pressure on the piston.

. While my invention is susceptible ofembodiment intools of manydifferent constructions I have shown in the drawings and will hereindescribe in detail one particular .emboc'fment of the invention which Iprefer to use, but I would have it understood that I and do not therebyintend to limit the invention in any way to the present particulardisclosure but aim to cover in the appended claims any modifications orequivalents falling within the scope of'the invention.

In the accompanying drawings Figure 1 is a longitudinal centralsectional view through a pneumatic hammer embodying the features of myinvention.

2 is a fragmentary sectional view on an enlarged scale, similar in allrespects to Fig. 1 except that the valve is shown in another position.

3 is a fragmentary sectional view of thevalve casing taken in tl e planeof line 3 '7, showing the venting port 27.

is a transverse section on line t l 1.

' is a view similar to F 1 but taken different axial plane through thetool. Big. 6 is an enlarged view similar to Fig. but show'ng the valvein a different position.

7 is a transverse section taken in the plane of line 7'. of Fig. 6. Theaxial plane on which F igs. 1 and 2 are taken is designated by the line2-2 in Fig. 7, while the plane of Figs. 5 and 6 is indicated by line6-6.'

Referring to the exemplary embodiment of my invention which I havechosen to disclose herein the tubular body or cylinder of the tool isdesignated by numeral 10 and the reciprocatory piston therein by numeral11. In the forward end of the cylinder is fitted the usual rivet set oranalogous working tool 12. 7 At the rear end of the body is the usualhandle 13 having a tubular head 14 which may be mounted on the body inany preferred manner, as by means of screw threads. The handle has theusual supply passage 15 for the live motive fluid which passageiscontrolled by a manually operated throttle valve, the lever of whichis designated 16.

Vfithin the rear end of the body 10 and the hea d 14- is a tubular valvecasing' 17 which in the present instance comprises a forward section 17fitting within a counter bore in the rear end of the body 10, and a rearsection 1'7 which intcrengages with the forward portion and lies betweenthe latter and the end wall of the handle head 14, the two part valvecasing being clamped securely in place by the handle. and being securedagainst rotation by a dowel pin 17 (Fig. 3).

A tubular valve member 18 fits slidably within the valve casing and hasa plurality of external annular flanges thereon forming shouldersagainst which the pressure of the motive fluid is exerted to move thevalve member in opposite directions.

Surroundingthe rear portion of the valve casing within the handle headis an annular chamber 19 which is constantly supplied with live in 1 lthe main Fig.

ive time passage 15 in the handle. The valve casing is provided with asuitable inlet means 20 connecting the annular chamber 19 with theinterior of the valve casing and the piston chamber, which inlet meansin the present instance is in the form ofa series of ports communicatingat their inner end with a narrower annular, groove When the valve member18 is in its forward position as shown in Fig. 1 the inlet 20 is exposedto admit live motive fluid into the piston chamber for driving thepiston forwardly.

A suitable number of passages 21 (see Figs. 5 and 6) drilledlongitudinally in the wall of the body 10 and in the valve casingcommunicate at their forward ends with-the extreme forward end of thepiston chamber and at their rear ends with an internal annular valvechamber 22 formed between the valve .iember and its casing, and thisannular chamber, when the valve is in its forward-w position as seen inFig. 5, is in communication with another annular chamber 23 which constantly communicates with the atmosphere through exhaust ports 24 in thevalve casing and body 10, the outer ends of said ports opening into aspace defined by the annular locking clip 14; by which the handle issecured to the body 10. V

It will thus be seen that when the valve member is in its forwardposition as seen in Figs. 1 and 5, live air will be admitted to the rearend of the piston chamber, and the previous charge of air will beexhausted from the forward end of said chamber a through the passages21, annular chambers 22 and 23, and ports 2a to the atmosphere.

The valve member has been moved to its forward position and is so heldby pressure within a rear valve chamber 25 (Figs. 1 and which is formedbetween the valve casing and the valve member, the forward wall of saidchamber being provided by an external flange 26 on the valve member. Therear portion of this chamber is connected with the interior of thepiston chamber at a point forward of the front end of the valve memberby means of a passage 27 (Fig. 3) which in the present instance isformed partially in the valve casing and partially in the cylinder 10.The chamber 25 is also in constant communication with the source of livemotive fluid by means of a port 28 (Fig. 3) which in the presentinstance leads in from the annular supply chamber 19 and communicateswith the said valve chamber by opening into the passage 27.

A passage 29 which is formed in the body 10 and in the valve casing 17communicates its forward end with the piston chamber at about themid-portion of the latter and at its rear end with an internal annularvalve chamber 30 in which an external flange 31 on the valve membermoves. Between its ends the passage 29 is connected with the pistonchamber by a port 32 which is considerably smaller than the inlet at theforward end of the passage 29. The purpose of this port 32 willpresently appear.

The chamber 30 is in constantcommunica- 'tion with the rear end of apassage 33 formed in the body and the valve casing, the forward end ofsaid passage communicating with the piston chamber near the forward endof the latter. hen the piston in its forward movement uncovers the port32, live air leaks through said port into thepassage 29 and thence flowsinto the chamber 30 and the passage 33 and starts to build up pressurein said passages and chamber. When the piston in its further forwardmovement uncovers the forward end of the passage 29 which is much largerthan the port 32, the live air flows into the passage 29 and thence intothe valve chamber 30. The point at which the valve shifts, however, isdetermined by the position of the forward end of the piston, becauseuntil the forward end of the passage 33 is covered by the piston thepressure in the large pressure chamber 30 is vented to the atmospherethrough the forward passage the forward piston chamber and the passage21.- Thus if, as is sometimes the case, an extremely short piston isused, so that the forward end of the passage 29 is uncovered before theforward end of the passage 33 is covered by the piston, the latterpassage, actingto vent the large forward pressure area, prevents apremature shifting of the valve. Consequently the valve shifts only whenthe forward end of the piston is the proper distance from the rivet set12. After the initial rearward movement of the valve has taken place,the extreme forward end thereof becomes exposed to the live pressure inthe rear piston chamber and this high pressure accelerates the rearwardmovement of the valve.

As the valve shi ts rearwardly the inlet for the live motive fluid isclosed and the exhaust chamber 23 in the valve casing is exposed motivefluid in the rear portion of the piS- ton chambermay escape through theex haust ports 24.. The valve chamber is connected by a port 34 with oneof the exhaust ports 24-, said port 34 leading from the rearend of saidchamber and permitting the escape of any motive fluid therein so as toprevent interference with the rearward movement of the valve member. c

As the motive fluid exhausts from the rear portion of the piston chamberthrough the ports 24, the fluid in the port 2 is also exhausted into therear portion of the piston chamber and thence to the atmosphere therebyrelieving pressure in the rear valve chamber 26 as to facilitate therearward shift. mg movement of the valve member. The

to the piston chamber so that the port 27 is of larger size than theport 28, so as to. provide substantially unrestricted communicationbetween the chamber 26 and the piston chamber as compared with therelatively restricted communication provided by the port 28 betw en thesource of motive fluid supply and said chamber 26. Accordingly, thepressure in the rear pres; sure chamber, is relieved in spite of thefact that theinlet port 28 is in constant com munication therewith.

' As soon as the exhaust ports 24 are opened to the piston chamber themotive fluid in the piston chamber escapes to the atmos phere, but thevalve member in its rear pos tion closes the rear end of the passage 29so that the pressure fluid in the annular valve chamber 30, and in thepassage 33 (which latter is at this time closed by the piston 11.) isprevented from escaping to the piston chamber through the passage 29,and therefore the' pressure fluid acting on the flange 31 of the valvemember serves to hold the valve in its rear position. I 7

In its rear positionthe valve member also uncovers a port 35 whichconnects the main motive fluid supply chamber 19 vwith the internalvalve chamber 22 so that live motive fluid may pass through said portand into and through the passages 21 to the forward end of the pistonchamber to return the piston. The port 35, it will be observed, is ofrelatively small. size so that the volume of pressure fluid admitted tothe forward piston "chamber is relatively small. The impact thereof onthe piston, however, is sufficient to drive it rapidlv to the rear endof the piston chamber. Also in this position of the valve, the pressurein the rear piston chamber exhauststo the atmosphere through the groove23 and the ports 2% so that pressure upon the rear end of the valve isre lieved. As a result the pressure trapped in the passage 33 and in thevalve chamber 3 is sufficient to hold the valve in its rear p sition.

In its rearward or return, movement the piston uncovers the forward endof thepas sage 33, and one of two things happens. If the valve memberhas a loose fit in its casing, some air will have leaked past the flange31 and reduced the pressure in the passage 33 so that when this passageis uncovered the pressure in the forward piston chamber will be greaterand some motive fluid will flow into the passage; But, if the valvemember has a tight fit in the casing, the

pressure in the passage 33 will have been maintained and; it is probablethat some of it will flow reversely into the forward piston chambersince the .ressure therein supplied by the restricted port 35 is lowerthan th live pressure previously supplied to the passage 33 from therearcpiston' chamber. In either case, as the piston continues to travelrearwardly this pressure, being supplied by the restricted port 35,becomes reduced by expansion and gradually lowers until the pressure inthe valve chamber 30 is ust sulficient to hold the valve in its rearposition so that it offers a minimum force opposii'ip; the forwardshifting of the valve at the proper time. This occurs'when the pistoncovers the forward end of the passage 27 causing the pressure to buildup in this passage and in the rear piston chamber until it is highenough to overcome the reduced pressure on the large pressure area inthe chamber 30.

The operation of the tool may be briefly reviewed as follows:

Let it be assumed that the valve 18 is ill its forward position as shownin Figs. 1 and 5 and that the piston is at the rear end of the pistOnchamber. The valve is held in its forward position by the pressure inthe rear valve chamber 25 which is constantly main tained by live motivefluid through the portconnection 27, 28, wit-h the live motive fluidsupply chamber 19. The live motive fluid entering the rear end of thepiston chamber through. the port 20, obviously acts upon 'illiu rear endof the valve member so as to assist in. holding the valve member in itsforward position. The inlet 20 being exposed, live motive fluid entersthe rear end of the piston chamber through said inlet and drives thepiston forwardly, the previous charge oi spent motive fluid beingexhausted from the front end of the piston chamber through the passages21, the chambers 22 and 23, and the exhaust ports 24 to the atmospher Inthe forward movement of the piston, the port 32 and the front end of thepassage 29 are successively uncovered by the rear end of the piston. Theport 32 allows the pressure to egin to build up in the passage 29,chamber 30 and passage 33, such pressure being augmented when theforward end of the passage 29 is uncovered by the piston.

The provision of the port 32 which causes a preliminary building up ofthe pressure in the valve chamber 30, makes it possible to extend thepassage 29 so as to communicate with the piston chamber at a. pointfarther forward than would be possible without the provision of the portIt is highly advantageous to have the passage 29 extend as far forwardas possible so that the full force of the charge of live motive fluid inthe piston chamber may be exerted upon the piston during as much of theforward stroke as possible.

In tools of this character as heretofore manufactured, however, therehas been a practical limit to the forward extent of a passage such asthe passage 29 since it is nec essary to allow time for the passage andthe valve chamber to fill with motive fluid and build up pressuresutiicient to shift the valve rearwardly. If the passage were carriedfarther forward than this practical limit, the result would be areduction in the speed of reciprocation of the piston, and a verydecided increase in the vibration of the tool with a resultant shockupon the operators hand and arm.

iVith a tool build in accordance with my invention, the passage 29 maybe carried forward as far as desired so as to utilize the power behindthe piston to the full proportion of its travel, and not only will thespeed of reciprocation of the piston not be slachened but it will beincreased because the port 32 allows a preliminary building up ofpressure in the valve chamber 30, leaving the final rise of pressure tobe accom plished when the forward end of the passage 29 is uncovered.The ultimate result accomplished is that heavier blows are de livered bythe piston at an increased ate of speed.

V] hen the forward end of the passage 29 is uncovered, the forward endof the passage 33 being closed, the pressure in the valve chamber 30will be sui'iicientto shift the valve member 18 rearwardly, but thiscannot occur until the forward end of the passage 3-3 is closed by thefront end of the piston to prevent the escape of motive fluid deliveredto the chamber 30 by the passage 29. Thus the point at which the valveis shifted is determined by the position of the piston with respect tothe forward end of the passage 33.

As soon as the front end of the valve member in its rearward movementexposes the chamber or groove 23 in the valve casing, the motive fluidin the rear portion of the piston chamber escapes through the exhaustports 2% to the atmosphere, thus relieving the pressure upon the rearend of the valve member. The fluid in the rear valve chamber 25 alsoescapes through the passage 27 into the piston chamber and thence to theatmosphere so that the pressure in the rear valve chamber 25 is greatlyreduced to speed up the movement of the valve.

'l Vhen in its rear position, the valve member closes the live motivefluid inlet 20 and connects the port 35 with the chamber 22 and thepassages 21 so that a restricted volume of live motive fluid passes fromthe annular supply chamber 19 through said port and passages to theforward end of the piston chamber so as to move the rearwardly.

When the rear end of the piston in its rearward travel closes the frontend of the passage 27 the pressure in the rear valve chamber 25 buildsup by reason of the sup ply of live motive fluid to such chamber throughthe port 28 so that the pressure overcomes thev opposing pressure on thefront flange 31, which pressure has been piston minimized by thereduction of pressure in the forward piston chamber due to the expansionof the fluid and shifts the valve forwardly before the piston reachesthe rear end of the )iston chamber. Live motive fluid is thusimmediately introduced into the rear end of the piston chamber so as tocushion the piston at the rear end of its stroke and immediately reversethe Piston and move it on its Working stroke again.v

In pneumatic hammers as previously manufactured, it was found necessaryto provide an auxiliary live motive fluid passage connecting the supplyof live motive fluid with the front valve chamber 30 for the purpose ofholding the valve in its rear position. The use of such auxiliarypassage for live motive fluid for this purpose is objectionable but hasheretofore been found to be necessary in order to maintain the pressurein the front valve chamber. to a sufficient degree to hold the valveinvits rear position. lVith the construction herein disclosed, thenecessity for such auxiliary passage has been entirely eliminated and byarranging the valve member so that it closes the rear end of the passage29 when the valve is in its rear position, I am able to maintain thevalve in its rear position in a positive manner and yet with a. minimumpressure so that it offers less resistance to the forward shifting ofthe valve when the time for i such shifting arrives. r The effectivepressure which tends to move the valve forwardly is thereby greatlyincreased so that a more prompt, quick and positive shifting of thevalve results and reliable action is insured whether the valve fitsquite tightly in its casing or fits rather loosely. The re suit is thatthe extreme nicety offit of the valve in its casing which has heretoforebeen indispensable is not necessary with the present construction, andthe life of the tool is greatly lengthened since satisfactory operationis not interfered with by considerable wear on the valve memberv and itscasing.

Similarly, in the shifting of the valve to its rear position,thepressure' in the rear valve chamber 25 is greatly reduced ventingsuch chamber through the passage 27 so that the effective pressuretending to, shift the valve rearwardly is materially increased which hasthe same effect as that above discussed of insuring promptness. speedand positiveness in the shifting of the valve, eliminating the necessityof extreme accuracy in the fitting thereof and adding life to the tool.

The result of the improved structure is that the efficiency of the toolas a whole is greatly enhanced because of the power always present forshifting. the valve whether. it fits tightly or loosely, and thedurability of the'tool is greatly increased because the valve will standconsiderable wear with the resulting looseness in fit without effectingits operation 1n ur1ously.

Furthermore, the structure as a Whole is simplified so that it ischeaper to manufacture than prior tools.

I claim as my invention: I

1. In a pressure fluid operated tool having a piston chamber and apiston reciprocable therein, a reciprocatory valve having a forwardpressure surface, a chamber communicatingwith said surface, a passagecon the pressure fluid thus admitted through said passage wherebyto holdthe valve member in its rear position, and means to relieve the 7pressure on said pressure surface in the return stroke of the piston.

2. In a fluid pressure actuated tool, in combination, a cylinder, apiston and a valve mechanism comprising a tubularcasing and valve memberthrough which the piston, reciprocates, the valve mechanism having.achamber to receive motive fluid for shiftingthe valve member rearwardlywhich chamber is arranged to be placed in communication with themid-portion of the interior ofthepiston chamber by neans of a passage,the forward end of said passage being arranged tov be uncovered by thepiston in its forward travel so as toadmit motive fluid through saidpassage to said chamber,

the rear end of such passage being arranged to be closed by the valvemember when in its rear position to prevent escape ,of the fluid. fromthe chamber back through said passage so as to holdthe valve member inits rear position, said valve chamber also -commun1cat1ng w1th a passagewhich is arranged to be filled with fluid from the valve chamber, thelatter passage communicating with the forward portion of the pistonchamber. c r

In a pressure fluid operated tool having a piston chamber and a pistonreciprocable therein, a valve mechanism comprising a movable valvemember in combination with a pressure chamber a d a passage forsupplying live motive fluid from the piston chamber to said pressurechamber in successive stages, said passage being cut oil by the movablevalve, member in its rear position to prevent escape of the fluid fromthe chamber back through said passage, and means to relieve the pressurein said pressure chamber. in the. forward stroke of the piston. 1 g v j4. In a pressure fluid operated tool having a piston chamber and apiston reciprocable therein, avalve mechanism comprising a valve memberand a pressure chamber in combination with means including a passage foradmitting live motive fluid from the piston chamber to said pressurechamber in successive stages, and a second passage from said pressurechamber to the forward end of the piston chamber adapted to be closed bythe piston in its forward position, said first mentioned passage beingcut oil by the movable valve member in its rear position to trap motivefluid in said pressure chamber and said second passage.

5. In a pressure fluid operated tool of the character described, thecombination of a cylinder forming a piston chamber, a piston, a controlvalve, a large valve chamber for receiving pressure fluid to shift saidvalve, a passage connecting said valve chamber with the forward end ofthe piston chamber and adapted to be closed by the piston in its forwardposition, and means for admitting pressure fluid in successive stagesfrom said piston chamber to said valve chamber for moving the valve inone direction.

6. In a pressure fluid operatedtool of the character described, thecombination of a cylinder forming a piston chamber, a piston, a controlvalve, a valve chamber adapted to receive pressure fluid to shift saidvalve in one direction, a passage connecting with said valve chamber,and means for admitting pressure fluid in successive stages from saidpiston chamber to said valve chamber and passage first to build uppressure in said chamber and passage and then to move the valve in onedirection.

7. In a pressure fluid operated tool of the character described thecombination of a cylinder forming a piston chamber, a piston, a controlvalve, a valve chamber adapted to receive pressure fluid to shift saidvalve, a chamber connecting with said valve chamber, and means foradmitting pressure fluid in successive stages from said piston chamberto said valve chamber and connecting chamber first to build up pressurein said chambers and then to move the valve in one direction, said valvein its movement operating to trap pressure fluid in said chambers.

8. A pressure fluid actuated tool having a cylinder forming a pistonchamber, a piston reeiprocable in said piston chamber, and means forcontrolling the movements of the piston including a movable valve member, a small pressure chamber and a large pressure chamber, a passage inconstant communication with a source of pressure fluid supplyestablishing restricted communication between said small pressurechamber and the rear piston chamber under the control of the piston, asecond passage arranged to discharge pressure fluid from the pistonchamber to the larger pressure controlling the movements of the pistoncomprising a movable valve member, means tending to hold the valvemember in position to admit pressure fluid to the rear piston chamber,said means comprising a small pressure chamber in constant butrestricted communication with a source of live pressure fluid, and apassage for gradually exhausting motive fluid from the small pressurechamber under the control of the piston, and means for reversing theposition ofthe valve member and holding it in such position comprising alarge pressure chamber, a passage controlled by the piston and in valvecontrolled communication with said large pressure chamber, and a thirdpassage communicating at all times with the larger pressure chamber andwith the forward piston chamber under the control of the piston.

10.111 a pressure-fluid-operated tool, a

valve mechanism comprisingv a movable valve member and means to actuatesaid valve including a pressure chamber adjacent said valve member, alive motive fluid su ply chamber in constant communication with saidpressure chamber, and a passage adapted gradually to exhaust motivefluid from said pressure chamber, said passage being unde'rthe controlof the piston whereby in the forward travel of the piston the pressurein the small pressure chambe' is relievedrto facilitate the reversal ofthe valve member and in the rearward travel of the piston the pressurein the small pressure chamber is built up to effect the movement of thevalve into its initial position.

11. In a pressure-fluid-operated tool, a valve mechanism comprising amovable valve member and having a pressure chamber for shifting saidvalve member, a live motive fluid supply chamber in constantcommunication with said pressure chamber, and a restricted passageadapted to exhaust motive fluid from said pressure chamber, said passagebeing under the control of the piston whereby in the forward travel ofthe piston the pressure in the small press re chamber-is relieved tofacilitate the reversal of the valve member, means for effecting the rversal of the valve member including a large pressure chamber, and meanstending to hold the valve member in its reversed position comprisingapassage controlled by the piston when in its forward position andcommunicating with said large pressure chamber, said valve member beingadapted in its initial position to control the discharge of a charge ofmotive fluid to the last mentioned passage and in its reversed positionto trap such charge of motive fluid in said passage.

12. A pneumatic tool comprising a piston chamber, a piston reciprocabletherein, and means for controlling the movements of the pistoncomprising a valve member, means tending to move and hold the valvememher in. )osition to admit a char e of motive fluid to the rear pistonchamber, and means tending to move the valve member into and holding itin reverse position including a chamber, a passage opening into thepiston chamber substantially centrally thereof and adapted tocommunicate with said pressure chamber in the initial position ofthevalve member, and a second passage communicating at times with saidpressure chamber and adapted to discharge into the forward pistonchamber under the control of the piston whereby in the rearward travelof the piston the pressure in said pressure chamber may discharge intothe forward piston chamber to permit the movement of the valve memberinto its initial position by theflrst mentioned means.

13. A pressure-fluid-actuated tool comprising, in combination with apiston chamber having a piston reciprocable therein, valve mechanism forcontrolling the movements of the piston comprising a valve casing, avalve member having a small pressure area and a large pressure area,means for constantly admitting live motive fluid to the small pressurearea, means for admitting motive fluid from the piston chamber behindthe piston to the large pressure area to shift the valve, said valveoperating when shifted to trap a quantity of such fluid so as tomaintain a holding pressure upon said large pressure area, meanscontrolled by the piston in its forward travel for relieving thepressure upon the small pressure area, and means controlled by thepiston in its rearward travel for relieving the pressure upon the largepressure area.

14. A pressure-fluid-actuated tool comprising, in combination with acylinder having a piston and valve mchanism for-controlling the piston,said valve mechanism comprising a small pressure chamber and a largepressure chamber, means for admitting constantly a restricted supply oflive motive fluid to the small pressure chamber, means controlled by thepiston in its forward movement for substantially relieving the pressurein the smaller chamber, and separate means controlled by the piston asit approaches the end of its forward movement for admitting pressurefluid from the piston chamber behind the piston to the larger pressurechamber whereby to shift the valve member.

15. A pressure-fluid-actuated tool comprising in combination with acylinder having a piston and valve mechanism for controlling the piston,said valve mechanism comprising a small pressure chamber and a largepressure chamber, means for admitting cons antly a restricted supply oflive motive fluid to the small pressure chamber, means controlled by thepiston in its forward movement for relieving the pressure in the smallchamber, and separate means controlled by the piston in its forwardtravel for admitting a gradually increasing amount of pressure fluidfrom the piston chamber behind the piston to the larger pressure chamberwhereby to shift the valve member.

16. A pressure-fluid-actuated tool comprising, in combination with 'acylinder having a piston, valve mechanism for controlling the piston,said valve mechanism comprising a small pressure chamber and a largepressure chamber, means forfadmitting constantly a restricted supply oflive motive fluid to the small pressure chamber, means controlled by thepiston in its forward movement for relieving the pressure in the smallerchamber, and separate means controlled by the piston in its forwardtravel for admitting pressure fluid to th larger pressure chamberwhereby to shift the valve member, said valve member being operable insuch movement to trap a quantity of the motive fluid thus admittedwhereby to hold the valve member in its shifted position.

17. A pressurefluid-actuated tool of the type comprising a cylinder witha piston reciprocable therein, and valve mechanism for controlling thepiston comprising a small pressure chamber communicating with a sourceof live motive fluid supply and having a passage constantly incommunication therewith and adapted to exhaust into the piston chamberbehind the piston when the piston is in its forward position, such eX- 4haust of pressure fluid into the piston chamber being controlled by thepiston, and a large pressure chamber having a passage communicating withthe forward piston chamber whereby when. the piston approaches itsforward position the valve member is shifted.

18. A pressure-fluid-actuated tool of the type comprising a cylinderwith a piston reciprocable therein, and valve mechanism for controllingthe piston comprising a small pressure chamber communicating -with asource of live motive fluid supply but adapted to exhaust into thepiston chamber when the piston is in its forward position,

and a large pressure chamber communicat ing with the forward pistonchamber where by when the p ston approaches its forward pos1t1on thevalve member is shifted, said class described comprising a valve memberhaving opposed pressure surfaces, means to admit live pressure luid tothe piston means for admitting live pressure fluid to one of thepressure surface means for gradually decreasin the pressure thereon asthe piston travels in one direction, and means for gradually admitting aportion of the motive fluid utilized in thus actuating the piston to thelarger pressure surface to shift the valve member.

20. In a pressure-fluid-actuated tool, the combination of meansproviding a piston chamber having a piston reciprocable therein, a valvemechanism having apressure area,

a passage communicating withthe mid-portion of the piston chamber andwith said pressure area to supply pressure fluid to said area, and asecond passage also communicating with said pressure area and with theforward .end of the piston chamber, said second passage being adapted tovent the pressure from said pressure area to the forward piston chamberuntil said second pas sage is closed by the piston, whereby to con trolthe time of movement of the valve.

21. A pressure-fiuid-actuated tool comprising, in combination, a pistonchamber having a piston reciprocable therein, a controlling va vemechanism including a valve member, means controlled by the rear end ofthe piston as it moves forwardly whereby to supply pressure fluid to thevalve member and separate means controlled by the front end of thepiston as it approaches the forward end of the stroke to render thefirst mentioned means operative to shift the valve.

In testimony whereof, I have hereunto set i 1 1 n] m m ERNEST H. SHAFF.

